U.S. patent application number 11/792861 was filed with the patent office on 2008-04-03 for metallic pigment and coating material containing the same.
Invention is credited to Yasushi Takano.
Application Number | 20080081864 11/792861 |
Document ID | / |
Family ID | 36587711 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080081864 |
Kind Code |
A1 |
Takano; Yasushi |
April 3, 2008 |
Metallic Pigment and Coating Material Containing the Same
Abstract
Disclosed is a metallic pigment which enables to provide a
coating film with very brilliant appearance and excellent corrosion
resistance at the same time. Also disclosed is a coating material
containing such a metallic pigment. Specifically disclosed is a
metallic pigment which is composed of aluminum particles as the
base particles whose surfaces are covered with a coating-layer
composed of one or more layers. The outermost layer of the
coating-layer contains a polymer which is obtained by polymerizing
a monomer having a basic group and at least one polymerizable
double bond. The monomer may preferably contain nitrogen. The
metallic pigment may preferably be provided with a surface
modification layer. Also specifically disclosed is a coating
material containing such a metallic pigment.
Inventors: |
Takano; Yasushi; (Nara,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
36587711 |
Appl. No.: |
11/792861 |
Filed: |
November 28, 2005 |
PCT Filed: |
November 28, 2005 |
PCT NO: |
PCT/JP05/21760 |
371 Date: |
June 12, 2007 |
Current U.S.
Class: |
524/441 |
Current CPC
Class: |
C09C 1/644 20130101;
Y02P 20/582 20151101; C09C 1/64 20130101; C09D 5/29 20130101; C09D
5/035 20130101 |
Class at
Publication: |
524/441 |
International
Class: |
C08K 3/08 20060101
C08K003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2004 |
JP |
2004-364409 |
Claims
1. A metallic pigment composed of aluminum particles serving as
base particles and formed with a coating-layer of a single layer or
multiple layers covering the surfaces of said aluminum particles,
wherein the outermost layer of said coating-layer contains a
polymer obtained by polymerizing a monomer having a basic group and
at least one polymerizable double bond.
2. The metallic pigment according to claim 1, wherein said
coating-layer is of a single layer, and said coating-layer is
composed of a copolymer obtained by polymerizing at least two
materials selected from a group consisting of oligomers and
monomers each having at least one polymerizable double bond and a
monomer having a basic group and at least one polymerizable double
bond.
3. The metallic pigment according to claim 1, wherein said
coating-layer is of multiple layers, and at least one layer of said
coating-layer other than the outermost layer is composed of a
copolymer obtained by polymerizing at least two materials selected
from a group consisting of oligomers and monomers each having at
least one polymerizable double bond.
4. The metallic pigment according to claim 1, wherein said monomer
having said basic group and at least one polymerizable double bond
is a compound containing nitrogen.
5. The metallic pigment according to claim 1, wherein said
coating-layer is formed to be in the range of 5 to 100 parts by
mass with respect to 100 parts by mass of aluminum particles.
6. The metallic pigment according to claim 1, wherein a surface
modifier layer is formed on the outer side of said
coating-layer.
7. The metallic pigment according to claim 6, wherein said surface
modifier layer contains a copolymer comprising a bond unit derived
from a fluoric polymerizable monomer having an alkyl fluoride group
and another bond unit derived from a polymerizable monomer having a
phosphoric acid group.
8. A coating material containing the metallic pigment according to
any of claims 1 to 7.
Description
TECHNICAL FIELD
[0001] The present invention relates to a metallic pigment
compatibly having high brilliance and corrosion resistance and a
coating material containing this metallic pigment. More
specifically, the present invention relates to a metallic pigment
capable of excellently maintaining corrosion resistance also when a
surface modifier layer is formed on the metallic pigment for
improving brilliance of a coating film and a powder coating
material containing this metallic pigment.
BACKGROUND ART
[0002] In recent years, a powder coating composition, drawing
attention to the characteristics as a low-pollution coating
material using no organic solvent, has been increasingly demanded
in various industrial fields of automobile components, household
appliances, furnishings, machine tools, business and office
machines, building materials and toys.
[0003] The powder coating composition, generally employing no
organic solvent and causing neither environmental problem nor
disaster resulting from an organic solvent, can be regarded as a
coating composition friendly to the global environment and humans.
Further, the powder coating composition can be relatively easily
recovered or cleaned with no working environmental pollution
resulting from scattering/adherence in application dissimilarly to
a solvent-type coating composition. In addition, the powder coating
composition causes no wastewater treatment problem dissimilarly to
a water-soluble coating composition.
[0004] A coating film formed by single application of the powder
coating composition has a large thickness to require no repetitive
wet-on-wet coating dissimilarly to a conventional solvent-type
coating composition, whereby the application time can be reduced.
Further, the powder coating composition contains no solvent in the
coating composition, to hardly form pinholes in the coating
film.
[0005] In the operation of applying the powder coating composition,
further, an oversprayed coating composition can be so recovered and
recycled that loss of the coating composition can be remarkably
reduced, thereby reducing the cost for the application step.
[0006] In general, a powder coating composition has mostly
contained no metallic pigment such as metallic powder. In such a
powder coating composition containing no metallic powder,
applicability and coating film characteristics of the powder
coating composition have been generally excellent and not
remarkably inferior to those of a general solvent-type coating
composition.
[0007] In recent years, demand for a metallic coating film
excellent in appearance has been increasing in various industrial
fields such as the automobile industry, due to refinement of the
aesthetic sense of consumers following improvement in the standards
of living. In order to satisfy such requirement of the consumers, a
powder coating composition providing a metallic coating film having
high designability, i.e., a powder metallic coating composition
formed by a powder coating material containing a metallic pigment
has been developed and positively introduced into several
industrial fields.
[0008] However, the powder coating composition containing a
metallic pigment has such a disadvantage that the color tone of a
coating film is darkened and no sufficient metallic feel is
attained if the metallic pigment cannot be arranged in parallel
with a substrate of the coating film. In order to overcome such a
disadvantage of the powder metallic pigment composition, therefore,
many efforts at research and development have been made in various
fields.
[0009] Generally developed methods of preparing powder metallic
coating compositions include melt blending previously sufficiently
kneading a metallic flake pigment with resin or a coloring pigment
by a melt process and thereafter pulverizing the mixture by
crushing or the like, dry blending mixing resin powder and a flake
pigment with each other and applying the mixture, a bonded process
using resin powder containing a metallic flake pigment adhering to
the surface thereof and the like (Japanese Patent Laying-Open No.
51-137725 (Patent Document 1), Japanese Patent Publication No.
57-035214 (Patent Document 2), Japanese Patent Laying-Open No.
09-071734 (Patent Document 3), U.S. Pat. No. 4,138,511 (Patent
Document 4) etc.).
[0010] In the melt blending, however, the metallic pigment is
easily deformed in the kneading step or a subsequent step of
adjusting the particle size of the resin powder by crushing or the
like. Therefore, the appearance of a coating film obtained by
applying the powder metallic coating composition prepared according
to this method cannot be regarded as sufficiently excellent. If the
metallic pigment is prepared from aluminum particles in this
method, further, active surfaces of aluminum are disadvantageously
exposed in the crushing step to result in a strong possibility of
ignition or dust explosion.
[0011] The dry blending has such an advantage that the metallic
pigment is relatively hardly deformed. However, the metallic
pigment must be charged in application if the powder coating
composition is electrostatically applied, and hence the surface of
the metallic pigment must be previously coated with resin when a
metallic pigment composed of aluminum particles or the like is
employed as the metallic pigment. Further, the resin powder and the
metallic pigment easily separate from each other in application due
to the different rates of charge of the metallic pigment and the
resin powder. Therefore, designability of the coating film is
reduced and the content of the metallic pigment in the powder
coating composition varies before and after application, to result
in such a problem that the coating material cannot be recycled in
practice since the color tone changes if the coating material is
reused upon recovery.
[0012] The bonded process includes a method bonding the metallic
pigment to the surface of the resin powder with a brushing polisher
or a method transferring and bonding the metallic pigment to the
resin powder by bringing the resin powder into contact with a
dispersion medium of alumina balls or the like covered with the
metallic pigment. This process has such a merit that the rate of
introduction of the metallic pigment into a coating film is so
stable that the powder coating composition recovered in a state not
bonded to a substrate can be recycled.
[0013] In this bonded process, however, the metallic pigment and
the resin powder are brought into pressure contact with/bonded to
each other through physical stress, and hence the metallic pigment
is so easily deformed that excellent metallic feel is hardly
obtained. Although resin particles advantageously hardly cause
bonding (blocking) due to small bonding strength, further, it is
difficult to bond the overall metallic pigment irregular in
particle size distribution to the resin powder in practice and
hence a large quantity of free particles of the metallic pigment
remain unbonded to the resin powder.
[0014] When the quantity of the free particles of the metallic
pigment is increased, the compounding ratio between the resin
powder and the metallic pigment so varies when the coating material
is recovered and reused that the coating material cannot be
recycled after the recovery similarly to that employed in the dry
blending. If a metallic pigment composed of aluminum particles or
the like is employed as the metallic pigment, further, a large
quantity of free particles are present, in the metallic pigment, to
result in a strong possibility of ignition or dust explosion.
[0015] The bonding strength between the resin powder and the
metallic pigment is remarkably reduced particularly when the
metallic pigment has a large particle diameter, and excellent
brightness and high brilliance attained only through employment of
the metallic pigment having a large particle diameter cannot be
easily attained in bonded aluminum obtained by this process.
[0016] In order to solve these problems, the inventor et al. have
developed a powder coating composition containing thermosetting
resin powder prepared by bonding aluminum flakes to the surface
through a specific bonding agent (International Patent Publication
No. 02/094950 (Patent Document 5)). According to this invention, a
recyclable uniform coating film exhibiting no color shading is
obtained and a pigment having a large particle diameter can be
used, whereby brilliance having been unattainable in the
conventional bonded process can be attained. However, this
brilliance is not remarkably improved as compared with the dry
blending.
[0017] In order to solve this problem, the inventor has already
invented a surface modifier composed of a resin composition
containing a copolymer comprising a bond unit derived from a
fluoric polymerizable monomer having an alkyl fluoride group and
another bond unit derived from a polymerizable monomer having a
phosphoric acid group. According to this method, a coating film
excellent in brightness can be obtained. Although a proper coverage
for a metallic pigment with this surface modifier is an extremely
small quantity of several milligrams/m.sup.2, electrostatic coating
can be performed with the coverage of such a small quantity. The
metallic pigment must be charged if the powder coating composition
is electrostatically applied by dry blending as described above,
and hence the surface of the metallic pigment must be previously
coated with resin when a metallic pigment composed of aluminum
particles or the like is employed as the metallic pigment. If the
aforementioned surface modifier is employed, however, electrostatic
coating can be performed with a small coat of the surface modifier
even if the surface of the metallic pigment is not previously
coated with resin.
[0018] On the other hand, high corrosion resistance is required in
addition to the aforementioned brightness when the powder coating
composition is utilized in practice. A coating film formed by
single application of a powder coating composition has a large
thickness to require no repetitive wet-on-wet coating dissimilarly
to a conventional solvent-type coating composition as described
above, whereby single baking of single application referred to as
one-coat one-bake forms the mainstream. Thus, the application cost
can be reduced as one of remarkable merits of the powder coating
composition. In this application method, however, no overcoat layer
is present on the outermost layer of the coating film and hence the
metallic pigment is directly exposed to external stimulation such
as a rainfall (particularly acid rain), washing with an alkaline
detergent, ultraviolet exposure or a high temperature/high
moisture. Therefore, corrosion of the pigment and following
discoloration of the coating film are more easily caused as
compared with a generally overcoated oil or water coating pigment,
and higher corrosion resistance is required to the pigment.
[0019] As a method of improving corrosion resistance of a pigment,
Japanese Patent Laying-Open No. 64-040566 (Patent Document 6), for
example, proposes a method of uniformly covering a pigment with a
copolymer obtained by reacting at least two materials selected from
a group consisting of oligomers and polymers each having at least
one polymerizable double bond. However, it is difficult to obtain a
coating film excellent in brilliance only according to this method.
While brilliance of a coating-film is recognizably improved to a
certain extent when the metallic pigment obtained according to the
method of Patent Document 6 is treated with the aforementioned
surface modifier and electrostatically applied, the effect of
improving brilliance in this case cannot sufficiently derive the
effect of the surface modifier, and no coating film having high
brightness required thereto is obtained. In other words, a
resin-coated coating film improving corrosion resistance so
inhibits the brilliance improving effect of the surface modifier
that no brilliance of an expectable level can be attained. Further,
a small-quantity coating film of the surface modifier itself has no
effect of improving corrosion resistance.
[0020] While powder metallic coating materials are prepared by
various methods as described above, none of the methods can provide
a coating film compatibly attaining metallic feel and brightness
providing a sufficiently satisfactory color tone and corrosion
resistance at the same time.
Patent Document 1: Japanese Patent Laying-Open No. 51-137725
Patent Document 2: Japanese Patent Publication No. 57-035214
Patent Document 3: Japanese Patent Laying-Open No. 09-071734
Patent Document 4: U.S. Pat. No. 4,138,511
Patent Document 5: International Patent Publication No.
02/094950
Patent Document 6: Japanese Patent Laying-Open No. 64-040566
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0021] An object of the present invention is to provide a metallic
pigment supplying a coating film with excellent metallic feel and
high brightness as well as excellent corrosion resistance at the
same time, and a coating material, particularly preferably a powder
coating material, containing this metallic pigment.
Means for Solving the Problems
[0022] The present invention relates to a metallic pigment provided
with a coating-layer of a single layer or multiple layers covering
the surfaces of aluminum particles characterized in that the
outermost layer of the coating-layer contains a polymer obtained by
polymerizing a monomer having a basic group and at least one
polymerizable double bond, and a coating material containing this
metallic pigment.
[0023] If the coating-layer is of the single layer, the
coating-layer is preferably composed of a copolymer obtained by
polymerizing at least two materials selected from a group
consisting of oligomers and monomers each having at least one
polymerizable double bond.
[0024] If the coating-layer is of multiple layers, at least one
layer of the coating-layer other than the outermost layer is
preferably composed of a copolymer obtained by polymerizing at
least two materials selected from a group consisting of oligomers
and monomers each having at least one polymerizable double
bond.
[0025] The monomer having the basic group and at least one
polymerizable double bond is preferably a compound containing
nitrogen.
[0026] In the metallic pigment according to the present invention,
the coating-layer is preferably formed to be in the range of 5 to
100 parts by mass with respect to 100 parts by mass of aluminum
particles.
[0027] In the present invention, a surface modifier layer is
preferably formed on the outer side of the coating-layer. In this
case, the surface modifier layer preferably contains a copolymer
comprising a bond unit derived from a fluoric polymerizable monomer
having an alkyl fluoride group and another bond unit derived from a
polymerizable monomer having a phosphoric acid group.
EFFECTS OF THE INVENTION
[0028] Brilliance and corrosion resistance of the metallic pigment
according to the present invention can be simultaneously improved
by forming the coating-layer containing the polymer obtained by
polymerizing the monomer having a basic group and at least one
polymerizable double bond on the surfaces of the aluminum particles
thereby increasing adhesiveness between a surface modifier and the
coating-layer particularly when the surface modifier is
employed.
BEST MODES FOR CARRYING OUT THE INVENTION
[0029] The present invention is now described in more detail with
reference to an embodiment.
[0030] <Aluminum Particles>
[0031] The metallic pigment according to the present invention is
composed of aluminum particles serving as base particles. This is
because aluminum has such excellent characteristics that the same
is excellent in metallic luster, low-priced and easy to handle due
to the small specific gravity. As to the material for the base
aluminum particles in the present invention, the main component,
i.e., the component occupying at least 50 mass % of the whole may
be aluminum, while the purity of aluminum is more preferably at
least 99.3 mass %, and pure aluminum is particularly preferable.
This is because the metallic luster of the metallic pigment is
particularly improved if the purity of aluminum is at least 99.3
mass %. If the aluminum particles contain a component other than
aluminum, an alloy of aluminum and another metal is preferably
employed. As an example of the metal alloyed with aluminum, at
least one metal selected from a group consisting of metals such as
zinc, copper, bronze (copper-tin alloy), nickel, titanium and
stainless can be preferably listed. An alloy of such a metal and
aluminum, having relatively excellent metallic luster, can be
preferably used as the base particles in the present invention.
[0032] The base aluminum particles in the present invention are not
restricted in shape but may have any shape such as a granular,
platy, bulk or flaky (scaly) shape, while the same are preferably
flaky in order to supply a coating film with excellent
brightness.
[0033] The average particle diameter of the base aluminum particles
is not particularly restricted but is preferably at least 1 .mu.m,
more preferably at least 3 .mu.m in particular. Further, the
average particle diameter of the base aluminum particles is
preferably not more than 100 .mu.m, more preferably not more than
50 .mu.m in particular. The base aluminum particles are difficult
to handle in preparation steps and tend to easily aggregate if the
average particle diameter of the base aluminum particles is less
than 1 .mu.m, while the surface of the coating film may be so
roughened when the metallic pigment is used as a coating material
that a preferable design cannot be implemented if the average
particle diameter exceeds 100 .mu.m.
[0034] The average thickness of the base aluminum particles is not
particularly restricted but is preferably at least 0.01 .mu.m, more
preferably at least 0.02 .mu.m in particular. Further, the average
thickness of the base aluminum particles is preferably not more
than 5 .mu.m, more preferably not more than 2 .mu.m in particular.
The base aluminum particles are difficult to handle in the
preparation steps and tend to easily aggregate if the average
thickness of the base aluminum particles is less than 0.01 .mu.m,
while particulate feeling of the coating film is so conspicuous or
hiding power is so insufficient that no preferable design can be
implemented if the average thickness exceeds 5 .mu.m.
[0035] The average particle diameter of the base aluminum particles
is obtained by calculating the volume average from particle size
distribution measured by a well-known particle size distribution
measuring method such as laser diffraction, micromesh sieving or a
Coulter counter method. The average thickness is calculated from
hiding power and density of the base aluminum particles.
[0036] A grinding lubricant added in grinding may be adsorbed to
the surfaces of the base aluminum particles. As an example of the
grinding lubricant, aliphatic acid such as oleic acid, stearic
acid, linoleic acid, linolenic acid, ricinoleic acid, elaidic acid,
zoomaric acid, gadoleic acid or erucic acid, aliphatic amine, fatty
amide, aliphatic alcohol, an ester or the like can be listed, for
example.
[0037] The grinding lubricant has an effect of suppressing
unnecessary oxidation of the surfaces of the base aluminum
particles and improving the luster. The quantity of adsorption of
the grinding lubricant varies with the application or the like, and
is not particularly restricted but is preferably not less than 2
parts by mass with respect to 100 parts by mass of the base
aluminum particles. Surface luster may be reduced if the quantity
exceeds 2 parts by mass.
[0038] Further, a coloring pigment layer or a coloring layer such
as an interference film may be formed on the surfaces of the base
aluminum particles. The base aluminum particles can be colored by
providing such coloring pigment layer or interference film, so that
a coating film having specific designability can be formed.
[0039] While a coloring pigment usable for providing the coloring
pigment layer is not particularly restricted, quinacridone,
diketopyrrolopyrrole, isoindolinone, indanthrone, perylene,
perinone, anthraquinone, dioxazine, benzoimidazolone,
triphenylmethanequinophthalone, anthrapyrimidine, chrome yellow,
pearl mica, transparent pearl mica, coloring mica, interference
mica, phthalocyanine, phthalocyanine halide, an azo pigment
(azomethine metal complex, condensed azo or the like), titanium
oxide, carbon black, iron oxide, copper phthalocyanine, a condensed
polycyclic pigment or the like can be listed, for example.
[0040] While a method of providing the interference film is not
particularly restricted, a method sputtering the surfaces of the
base aluminum particles with a thin film of a dissimilar metal can
be listed, for example. While the dissimilar metal employed at this
time is not particularly restricted, a copper alloy such as brass,
an iron alloy such as stainless steel or a nickel alloy such as
hastelloy can be listed in addition to gold, silver, copper,
nickel, cobalt, titanium or aluminum, for example.
[0041] A method of preparing the base aluminum particles is not
particularly restricted but the particles can be prepared by a
well-known method. As a specific example, a method of preparing
aluminum particles comprising the steps of preparing aluminum
powder, preferably aluminum spherical powder by gas atomization,
water atomization, a rotating disc method or melt spinning and
grinding the aluminum powder by well-known ball milling can be
listed.
[0042] <Raw Monomer for Forming Outermost Layer>
[0043] A polymer forming the outermost layer of the coating-layer
in the metallic pigment according to the present invention is
obtained by polymerization of a monomer having a basic group and at
least one polymerizable double bond, and generated as a polymer
(hereinafter referred to as a basic polymer) having basic points in
molecules. In the present invention, basic points denote electron
pair-donating sites. This polymer includes either a homopolymer or
a copolymer.
[0044] The reason why the coating film excellently compatibly
attains brilliance and corrosion resistance when a polymerizable
monomer having a basic group is used as the raw material for
forming the outermost layer of the coating-layer in the present
invention can be estimated as follows: In a metallic pigment
prepared by forming a surface modifier layer of a fluoric polymer
having a phosphoric acid group on the surfaces of aluminum
particles, affinity between another component in a coating material
and the surface of the metallic pigment is reduced due to
contribution of the polymer and the metallic pigment is oriented on
the surface of the coating film for improving brilliance of the
coating film while adsorptivity of the surface modifier layer for
the aluminum particles is improved due to contribution of the
phosphoric acid groups and the surface modifier layer is uniformly
formed.
[0045] When the coating-layer is formed between the base aluminum
particles and the surface modifier in order to further supply the
metallic pigment provided with the surface modifier layer with
corrosion resistance, adsorptivity between the surface modifier
layer and the coating-layer is so deteriorated that the surface
modifier layer is not uniformly formed and the polarity of
unadsorbable phosphoric acid groups may attenuate water repellency
of the fluoric polymer to reduce the brilliance of the coating film
if the interaction between the surface modifier layer and the
coating-layer is weak. In this case, the coating-layer interposed
between the base aluminum particles and the surface modifier layer
is not sufficiently effective. In the present invention, the basic
points serving as adsorption sites of the surface modifier layer
for the phosphoric acid groups can be formed on the surface of the
coating-layer by forming the coating-layer containing the polymer
obtained by polymerizing the monomer having the basic group.
Therefore, strong adsorption between the surface modifier layer and
the coating-layer can be attained due to acid-base interaction. The
phosphoric acid groups of the surface modifier layer are oriented
on the interfaces between the surface modifier layer and the
coating-layer due to this acid-base interaction, whereby the water
repellency of the fluoric polymer is so sufficiently exhibited that
high brilliance is conceivably implemented due to a leafing effect
upon formation of the coating film.
[0046] Therefore, the monomer having the basic group used in the
present invention, aimed at ensuring basic points on the surface of
the coating-layer, may simply satisfy such a condition that the
same is basic and can serve as a component of coating resin. In
consideration of industrial production, however, the monomer having
the basic group and at least one polymerizable double bond is
preferably a compound containing nitrogen in view of the cost and
polymerization. More specifically, (meth)acrylic ester of tertiary
amine, vinylpyridine, vinylpyrrolidone or the like is preferable,
and dimethylaminoethyl (meth)acrylate, diethylaminoethyl
(meth)acrylate or the like is more preferable. However, the present
invention is not restricted to these.
[0047] While the monomer serving as the raw material for forming
the outermost layer may contain only the polymerizable monomer
having the basic group and at least one polymerizable double bond,
this monomer may further contain another monomer or an oligomer. If
the coating-layer is of the single layer, at least two materials
selected from a group consisting of oligomers and monomers each
having at least one polymerizable double bond are preferably
contained in addition to the polymerizable monomer having the basic
group and at least one polymerizable double bond. In this case,
corrosion resistance of the metallic pigment can be further
improved.
[0048] The content of the polymerizable monomer having the basic
group and at least one polymerizable double bond is preferably at
least 5 mass %, particularly preferably 10 mass % of the overall
monomer and/or oligomer serving as the raw material for the polymer
forming the outermost layer. If the content is less than 5 mass %,
the metallic pigment tends to exhibit insufficient brilliance.
Further, this content is preferably not more than 90 mass %,
particularly preferably not more than 70 mass %. If this content
exceeds 90 mass %, corrosion resistance of a metallic coating
material may not be sufficiently attained.
[0049] <Monomer and/or Oligomer forming Inner Layer>
[0050] The metallic pigment according to the present invention is
supplied with excellent corrosion resistance also when only single
coating-layer is formed by a polymer obtained by polymerizing a
polymerizable monomer having the basic group and at least one
polymerizable double bond. However, it is preferable to form the
coating-layer of multiple layers having the outermost layer of the
polymer obtained by polymerizing the polymerizable monomer having
the basic group and at least one polymerizable double bond and to
form an inner layer of a polymer prepared from at least two
materials selected from the group consisting of oligomers and
monomers each having at least one polymerizable double bond between
the outermost layer and the base aluminum particles, in order to
attain stronger corrosion resistance. The monomer and the oligomer
are now described more specifically.
[0051] As an example of the monomer having at least one
polymerizable double bond, unsaturated carboxylic acid (acrylic
acid, methacrylic acid, crotonic acid, itaconic acid, citraconic
acid, maleic acid or maleic anhydride, for example), a nitrile
thereof (acrylonitrile or methacrylonitrile, for example) or an
ester thereof (methyl acrylate, ethyl acrylate, n-butyl acrylate,
2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate,
hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methoxyethyl
acrylate, butoxyethyl acrylate, glycidyl acrylate, cyclohexyl
acrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate,
trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate,
tetramethylolmethane triacrylate, methyl methacrylate, ethyl
methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate,
lauryl methacrylate, stearyl methacrylate, hydroxyethyl
methacrylate, 2-hydroxypropyl methacrylate, methoxyethyl
methacrylate, butoxyethyl methacrylate, glycidyl methacrylate,
cyclohexyl methacrylate, trimethylolpropane trimethacrylate or
tetramethylolmethane trimethacrylate, for example) is preferably
illustrated. Further, a cyclic unsaturated compound (cyclohexene,
for example), an acyclic unsaturated compound (styrene,
.alpha.-methylstyrene, vinyltoluene, divinylbenzene, cyclohexene
vinylmonoxide, divinylbenzene monoxide, vinyl acetate, vinyl
propionate or diallyl benzene, for example) or the like is also
preferable.
[0052] As an example of the oligomer having at least one
polymerizable double bond, epoxidized 1,2-polybutadiene, acrylic
denatured polyester, acrylic denatured polyether, acrylic denatured
urethane, acrylic denatured epoxy, acrylic denatured spiran or the
like (each having a polymerization degree of about 2 to 20) can be
illustrated. In particular, epoxidized 1,2-polybutadiene or acrylic
denatured polyester having a polymerization degree of 3 to 10 is
preferable. Employment of the oligomer is preferable in a point
that polymerization gradually progresses and reaction efficiency
remarkably increases.
[0053] When a monomer and/or an oligomer having at least two
polymerizable double bonds is used for the layer of the
coating-layer other than the outermost layer, the corrosion
resistance is particularly preferably further improved due to a
cross-linking action.
[0054] <Polymer Forming Outermost Layer>
[0055] The quantity of the overall coating-layer (total
coating-layer) according to the present invention including the
inner layer and the outermost layer is preferably at least 5 parts
by mass, more preferably at least 10 parts by mass in particular
with respect to 100 parts by mass of the base aluminum particles.
Further, the quantity of the total coating-layer is preferably not
more than 100 parts by mass, particularly preferably not more than
80 parts by mass. Sufficient corrosion resistance may not be
attainable if the quantity of the total coating-layer is less than
5 parts by mass, while the coating-layer may be so excessively
thick that reflected light from the metallic pigment is scattered
to reduce the brilliance of the coating film if the quantity of the
total coating-layer exceeds 100 parts by mass.
[0056] In the metallic pigment according to the present invention,
the surface of the base aluminum layer may be covered with the
coating-layer of the single layer formed by a layer containing a
basic polymer or a layer composed of only the basic polymer, or the
surfaces of the base aluminum particles may be covered with the
coating-layer of the multiple layers formed by the outermost layer
and the inner layer of another polymer, while the outermost layer
of the coating-layer is formed by a layer containing the basic
polymer obtained by polymerization of the monomer having the basic
group in either case.
[0057] While the layer containing the basic polymer may be formed
as a plurality of layers including outermost layer or the inner
layer may be formed as a plurality of layers in the present
invention, a single coating-layer or a coating-layer of a two-layer
structure formed by the inner layer and the outermost layer is
preferably employed in view of production efficiency.
[0058] In the present invention, a method of forming the
coating-layer of a single layer or multiple layers on the surface
of the base aluminum particles is not particularly restricted so
far as the same is a method capable of forming a uniform coating
film of a resin composition on the surfaces of metallic particles,
and a well-known method can be employed. More specifically, a
method of forming the coating-layer of a target polymer on the
surface of the base aluminum particles by dissolving a
polymerizable monomer and/or a polymerizable oligomer in an organic
solvent in which untreated aluminum particles are dispersed and
heating the same under coexistence of a polymerization initiator or
the like can be employed, for example.
[0059] Either the single layer or the multiple layers can be
employed as the coating-layer in the present invention. In a case
of forming the coating-layer of the multiple layers, there is a
method of forming multiple layers by forming a metallic pigment
provided with the single coating-layer by the aforementioned method
and thereafter stacking layers one by one by repeating an operation
of isolating the metallic pigment by filtration/washing. In
addition, there is also a method of continuously forming multiple
layers by adding another type of monomer and/or oligomer in an
intermediate stage of polymerization of a monomer and/or an
oligomer. In the present invention, a metallic pigment having
desired corrosion resistance and brilliance can be obtained by
either method, and the method of forming the coating-layer is not
restricted.
[0060] While the aforementioned organic solvent for dispersing
untreated aluminum particles is not particularly restricted, a
solvent not dissolving a generated basic polymer is preferably
employed. More specifically, an isoparaffin-based solvent, a
solvent of aliphatic hydrocarbon solvent such as hexane, heptane,
octane, nonane, decane, undecane or dodecane, a solvent of aromatic
hydrocarbon such as benzene, toluene or xylene, a solvent of ether
such as diethyl ether, a solvent of ester such as ethyl acetate or
butyl acetate, a solvent of alcohol such as methanol, ethanol,
butanol, glycerin or polypropylene glycol or the like can be
listed, for example. A single such organic solvent may be employed,
or at least two such organic solvents may be employed in a mixed
state.
[0061] The usage of the organic solvent is preferably at least 300
parts by mass, more preferably at least 400 parts by mass in
particular with respect to 100 parts by mass of the base aluminum
particles. Further, the usage of the organic solvent is preferably
not more than 1200 parts by mass, more preferably not more than 800
parts by mass in particular. The viscosity of the reaction liquid
is so excessively increased that the reaction components tend to be
difficult to uniformly diffuse if the usage of the organic solvent
is less than 300 parts by mass, while there is such a tendency that
a large quantity of unreacted monomer remains due to a low monomer
concentration even if the reaction time is increased if the usage
of the organic solvent exceeds 1200 parts by mass.
[0062] The aforementioned polymerization initiator is not
particularly restricted but that generally known as a radical
generator can be employed. As a specific example, peroxide such as
benzoyl peroxide, lauroyl peroxide, isobutyl peroxide or methyl
ethyl ketone peroxide or an azo compound such as
azobisisobutylonitrile (also abbreviated as "AIBN") can be
listed.
[0063] The compounding ratio of the polymerization initiator is
preferably at least 0.1 parts by mass, more preferably at least 0.5
parts by mass in particular with respect to 100 parts by mass of
the coating-layer. Further, the compounding ratio of the
polymerization initiator is preferably not more than 10 parts by
mass, more preferably not more than 8 parts by mass in particular.
Such a problem may arise that polymerization does not progress and
the coating-layer is not formed in a planned quantity if the
compounding ratio of the polymerization initiator is less than 0.1
parts by mass, while there is such a tendency that polymerization
so abruptly progresses that free polymer particles are formed to
abruptly increase viscosity of the overall system due to belated
adsorption of the generated polymer to the base aluminum particles
to result in aggregation of the reaction components as the case may
be if the compounding ratio exceeds 10 parts by mass.
[0064] The polymerization temperature of the monomer and/or the
oligomer is properly set in response to the type of the used
polymerization initiator. The half-value period of the
polymerization initiator is univocally decided in response to the
temperature, and such a temperature is preferable that the
half-value period of the polymerization initiator is at least 5
minutes, while such a temperature is more preferable in particular
that the half-value period of the polymerization initiator is at
least 15 minutes. Further, such a temperature is preferable that
the half-value period of the polymerization initiator is not more
than 20 hours, and such a temperature is more preferable in
particular that the half-value period of the polymerization
initiator is not more than 10 hours. When AIBN is employed as the
polymerization initiator, for example, half-value periods are 22
hours, 5 hours, 1.2 hours and 0.3 hours at 60.degree. C.,
70.degree. C., 80.degree. C. and 90.degree. C. respectively, and
hence a more preferable range of the polymerization temperature is
70 to 90.degree. C. Such a problem may arise that polymerization
does not easily progress if such a combination of a polymerization
temperature and a polymerization time is employed that the
half-value period of the polymerization initiator exceeds 20 hours,
while there is such a tendency that polymerization so abruptly
progresses that free polymer particles are formed to abruptly
increase viscosity of the overall system due to belated adsorption
of the generated polymer to the base aluminum particles to result
in aggregation of the reaction components as the case may be if
such a combination of a polymerization temperature and a
polymerization time is employed that the half-value period of the
polymerization initiator is shorter than 5 minutes. In order to
improve polymerization efficiency, it is favorable to perform the
polymerization under an atmosphere of inert gas such as nitrogen,
helium or argon.
[0065] Slurry containing the metallic pigment resulting from
completion of polymerization is converted to paste containing the
metallic pigment and the solvent by removing an excess solvent or
an unreacted monomer by filtration or centrifugation. The obtained
paste may be subjected to solvent washing if necessary. While the
paste may thereafter be converted to powder by completely removing
the solvent through a drying step, the metallic pigment is
generally completed in the paste state in view of operability.
[0066] <Surface Modifier>
[0067] A surface modifier layer is preferably-further formed on the
surface of the metallic pigment according to the present invention.
This surface modifier layer preferably has an action of orienting
the metallic pigment on the surface of a coating film in
application of a coating material containing the metallic pigment
by reducing affinity between the metallic pigment and another
coating component. In this case, the coating film can be supplied
with more excellent brilliance. As a preferable polymer forming the
surface modifier layer, that at least containing a copolymer
comprising a bond unit derived from a fluoric polymerizable monomer
having an alkyl fluoride group and another bond unit derived from a
polymerizable monomer having a phosphoric acid group or the like
can be listed. More preferably, a copolymer comprising the bond
unit derived from the said fluoric polymerizable monomer having the
alkyl fluoride group and the bond unit derived from the
polymerizable monomer having the phosphoric acid group as well as
still another bond unit derived from at least one polymerizable
monomer is employed.
[0068] Further preferably, such a copolymer can be listed that the
fluoric polymerizable monomer having the alkyl fluoride group is
perfluorooctylethyl acrylate, the polymerizable monomer having the
phosphoric acid group is 2-methacryloyloxyethyl acid phosphate or
2-acryloyloxyethyl acid phosphate and the bond unit derived from at
least one polymerizable monomer other than the bond unit derived
from the fluoric polymerizable monomer having the alkyl fluoride
group and the bond unit derived from the polymerizable monomer
having the phosphoric acid group is styrene or methyl
methacrylate.
[0069] In the polymer forming the surface modifier layer, the
content of the bond unit derived from the fluoric polymerizable
monomer having the alkyl fluoride group is preferably in the range
of 1 to 40 mol %, the content of the bond unit derived from the
polymerizable-monomer having the phosphoric acid group is
preferably in the range of 1 to 30 mol % and the number-average
molecular weight is preferably set in the range of 1000 to 500000,
while the polymer is not particularly restricted. This polymer is
preferably a copolymer soluble in a solvent. The content of a bond
unit in a fluoric polymerizable polymer can be measured by a flask
combustion method-ion chromatography or the like, for example, and
the content of the bond unit derived from the polymerizable monomer
having the phosphoric acid group can be evaluated by wet acid
decomposition-ICP (Inductively Coupled Plasma) analysis or the
like, for example. The number-average molecular weight can be
evaluated by gel permeation chromatography (GPC) or the like, for
example.
[0070] <Surface Treatment>
[0071] A surface modifier obtained by copolymerization is first
dissolved in a solvent, added to the metallic pigment according to
the present invention and kneaded. The surface modifier may be
directly added in the state of an unpurified liquid upon completion
of copolymerization, or may be added in a state diluted with a
dilution solvent. At this time, the metallic pigment may be in a
state of solventless powder or paste containing a solvent. The
content of the surface modifier is preferably set to 0.1 mass % to
5 mass % with respect to the mass of a nonvolatile component of the
metallic pigment, i.e., that obtained by removing the solvent from
the metallic pigment. The effect of improving brilliance of the
coating film by providing the surface modifier layer tends to
insufficiently appear if the content is less than 0.1 mass %, while
there is such a tendency that aggregation so easily arises in a
later pulverization step that a practical powder metallic pigment
is difficult to obtain if the content exceeds 5 mass %. However,
the content of the surface modifier is not restricted to this. The
solvent for dissolving the surface modifier is not particularly
restricted so far as the same is capable of dissolving the surface
modifier and exerts no bad influence on the properties of the
metallic pigment.
[0072] The usage of the solvent is preferably set to 10 mass % to
400 mass % with respect to the nonvolatile component of the
metallic pigment. There is such a tendency that uniform kneading is
difficult if the usage is less than 10 mass %, while there is such
a tendency that a large quantity of poor solvent must be used in a
dispersion step described later and hence production efficiency is
deteriorated if the usage exceeds 400 mass %. If the metallic
pigment is used as the paste containing the solvent, attention must
be given to calculation of the quantity of the solvent added with
the surface modifier. Since the surface modifier solution and the
paste are kneaded, a mixed solvent is employed in the mixed system.
Unless the mixed solvent has a composition dissolving the surface
modifier, the surface modifier is precipitated in the process of
kneading and inhibited from uniform adsorption to the metallic
pigment. Therefore, the usage of the solvent is preferably set to
provide a composition sufficiently dissolving the surface modifier
in the mixed system.
[0073] When a surface modifier having a phosphoric acid group is
used, phosphoric acid group portions in surface modifier molecules
are conceivably adsorbed to the metallic pigment in the process of
kneading of the metallic pigment and the surface modifier. While
this adsorption can be rendered more reliable when a method of
aging the paste after completion of kneading or a method performing
warm kneading or warm aging is employed, the effect of the surface
modifier sufficiently appears without specific operation and hence
the present invention is not particularly restricted.
[0074] Such surface modifier-containing paste can be obtained by
the aforementioned method that the surface modifier layer is
further formed on the surface of the metallic pigment according to
the present invention. In order to powder this paste, a technique
of filtrating and drying a material prepared by dispersing this
paste in a poor solvent with respect to the surface modifier is
encouraged. If the paste is dried as such, particles of the
metallic pigment may be bonded to each other to aggregate. While
sufficiently utilizable powder can be obtained by re-crushing also
in this case, such a problem may arise that the metallic pigment is
partially deformed in crushing. While the aforementioned problem of
aggregation can be avoided by washing the paste with a good solvent
and drying the same, there is such a tendency that the adsorbed
surface modifier is also gradually washed out and the effect
resulting from the provision of the surface modifier layer cannot
be sufficiently attained.
[0075] When the surface modifier-containing paste is gradually
introduced into a large quantity of strongly stirred poor solvent
for forming slurry and this slurry is filtrated and dried, the
problem of deformation or aggregation of the metallic pigment or
elution of the surface modifier can be avoided. In other words, the
metallic pigment is so dispersed in the dispersion solvent that the
particles thereof are not in contact with each other. At the same
time, the poor solvent extracts a good solvent so that the surface
modifier is precipitated on the surface of the metallic pigment as
a solid, whereby no mutual bonding results also when the particles
of the metallic pigment provided with the surface modifier layer
come into contact with each other again. Alkane such as hexane,
heptane or Merveille is preferable as the poor solvent for the
surface modifier.
[0076] <Powder Coating Material Preparation Method>
[0077] The metallic pigment according to the present invention can
form a powder coating material when blended into resin powder such
as thermosetting resin powder, for example. The type of the resin
powder is not particularly restricted but thermosetting resin
powder of a resin composition containing resin melted by heating
and thereafter quickly solidified and exerting no influence on the
metallic pigment according to the present invention can be
preferably employed.
[0078] Well-known thermosetting resin powder for powder coating can
be particularly preferably employed as the thermosetting resin
powder. As a specific example, powder of a resin composition
containing acrylic resin or polyester resin can be listed. A
hardener, a disperser or the like may be added to the thermosetting
resin powder employed for the powder coating material of the
present invention if necessary.
[0079] The hardener addable to the thermosetting resin powder is
not particularly restricted but a well-known hardener can be used.
As a specific example, amine, polyamide, dicyandiamide, imidazole,
dihydrazide carboxylate, acid anhydride, polysulfide, boron
trifluoride, amino resin, triglycidyl isocyanate, primide, epoxy
resin, other dibasic acid, imidazolyn, hidrazide, an isocyanate
compound or the like can be listed. A single such hardener may be
employed, or at least two such hardeners may be employed in a mixed
state. Further, this hardener can also be employed along with an
accelerator if necessary.
[0080] The disperser addable to the thermosetting resin powder is
not particularly restricted but a well-known disperser can be used.
As a specific example, a surface-active agent of phosphate, amine,
polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether or
the like can be listed. A single such disperser may be employed, or
at least two such dispersers may be employed in a mixed state.
[0081] In addition to the above, a filler of calcium carbonate,
barium sulfate or talc, a flowability regulator of silica, alumina
or aluminum hydroxide, a coloring pigment such as titanium oxide,
carbon black, iron oxide, copper phthalocyanine, an azo pigment or
a condensed polycyclic pigment, a flow leveler such as an acrylic
oligomer or silicone, a foaming inhibitor such as benzoin, an
additive such as wax, a coupling agent, an antioxidant or magnetic
powder and a functional material may be added to the thermosetting
resin powder if necessary.
[0082] The average particle diameter of the thermosetting resin
powder employed for the powder coating material according to the
present invention is not particularly restricted but is preferably
at least 5 am, more preferably at least 15 .mu.m in particular.
Further, this average particle diameter is preferably not more than
100 .mu.m, more preferably not more than 60 .mu.m in particular. If
the average particle diameter of the thermosetting resin powder is
less than 5 .mu.m, uniform dusting may be so difficult in powder
coating that a block of resin adheres to a coated plate and
smoothness is lost.
[0083] If the average particle diameter of the thermosetting resin
powder exceeds 100 .mu.m, on the other hand, smoothness of the
surface of the powder-coated coating film may be so inhibited that
no excellent appearance can be obtained.
[0084] In the powder coating material according to the present
invention, the content of the metallic pigment according to the
present invention is preferably at least 1 part by mass, more
preferably at least 2 parts by mass in particular with respect to
100 parts by mass of the thermosetting resin powder employed in the
present invention. Further, the content of this metallic pigment is
preferably not more than 40 parts by mass, more preferably not more
than 20 parts by mass in particular. If this content is less than 1
part by mass, no sufficient metallic feel and brightness may be
attainable and there is such a tendency that the thickness of the
coating film must be increased in order to conceal a substrate. If
this content exceeds 40 parts by mass, on the other hand, the cost
is increased, while there is such a tendency that smoothness of the
coating film is lost to deteriorate the appearance.
[0085] A method of preparing the powder coating material according
to the present invention is not particularly restricted but a
method of preparing a powder coating material by simply
dry-blending the metallic pigment with the thermosetting resin
powder for powder coating or the like can be preferably
employed.
[0086] <Powder Coating Method>
[0087] As a method of applying the powder coating material
according to the present invention, it is preferable to previously
blast the surface of a substrate to be coated, stick the powder
coating material after performing well-known treatment such as
chemical conversion and thereafter heat/harden the powder coating
material. While fluidized-bed coating, electrostatic powder coating
or the like can be applied as a method of sticking the powder
coating material to the surface of the substrate, electrostatic
powder coating is superior in coating efficiency and more
preferable. A well-known system such as a corona discharge system
or a frictional electrification system can be employed as the
system of electrostatic powder coating.
[0088] The heating temperature for heating/hardening the powder
coating material, properly settable in response to the type of the
employed thermosetting resin powder, may be generally set to at
least 120.degree. C., preferably 150 to 230.degree. C. The heating
time, properly selectable in response to the heating temperature,
may be generally set to at least one minute, preferably 5 to 30
minutes. The thickness of the coating film formed by heating, not
restrictive, is generally about 20 to 100 .mu.m.
[0089] <Method of Evaluating Brilliance of Coating Film>
[0090] In the present invention, brightness of the coating film can
be evaluated with an evaluation parameter .beta./.alpha.. This
evaluation parameter, i.e., .beta./.alpha. results from the
following expression (1): L=[.beta./(.theta.2+.alpha.)]+6.ident.
Expression (1) where L represents a lightness index (L*a*b*
colorimetric system (color system based on a uniform color space
set by CIE in 1976) measured with a spectrophotometer (trade name
"X-Rite MA68" by X-Rite) at an observation angle .theta., .theta.
represents the observation angle, and .alpha., .beta. and .gamma.
represent constants.
[0091] The first item of the expression (1) corresponds to
directional scattering specific to the metallic pigment depending
on the observation angle .theta., and the second item corresponds
to isotropic scattering not dependent on the observation angle
.theta.. Visual brilliance highly correlates with an L value on a
direct reflection position (.theta.=0) of directional scattering,
i.e. .beta./.alpha., and hence .beta./.alpha. is used as the
evaluation parameter for brightness.
[0092] In order to calculate .beta./.alpha., .alpha., .beta. and
.gamma. must be first decided. According to the present invention,
.alpha., .beta. and .gamma. can be decided by the method of least
squares by measuring actual L values at observation angles .theta.
of 15 degrees, 25 degrees, 45 degrees, 75 degrees and 10 degrees
and assuming that the relation between these .theta. and L values
satisfies the expression (1).
[0093] <Corrosion Resistance Evaluation>
[0094] The term corrosion resistance employed in the present
invention indicates chemical resistance (alkali resistance and acid
resistance) and weather resistance, aluminum is particularly easily
corroded by alkali, and evaluation of chemical resistance,
particularly alkali resistance is suitable as evaluation of the
metallic pigment according to the present invention based on
aluminum itself.
[0095] The metallic pigment according to the present invention can
simultaneously provide excellent corrosion resistance and high
brilliance, whereby a coating composition employing the metallic
pigment according to the present invention is applicable to coating
in various industrial fields, and preferably utilized for coating
of the bodies of automobiles or the like, office supplies,
household goods, sporting equipment, agricultural chemical
materials, electric appliances or the like, for example.
EXAMPLES
[0096] While the present invention is now described in more detail
with reference to Examples, the present invention is not restricted
to these.
Example 1
[0097] First, metallic pigment paste (trade name 7640NS by Toyo
Aluminum Kabushiki Kaisha) prepared from paste of aluminum flakes
was washed with mineral spirit and filtrated. The content of a
nonvolatile component in the paste subjected to washing and
filtration was 70.0 mass %.
[0098] 599.5 g of mineral spirit was added to 171.4 g of this paste
in a separable flask of 1 liter and stirred for preparing slurry.
While stirring was continued, the system was purged with nitrogen
gas to be under a nitrogen atmosphere and thereafter heated to
80.degree. C. The following operations were performed while
maintaining these conditions unless otherwise stated.
[0099] 0.85 g of acrylic acid, 8.3 g of epoxidized
1,2-polybutadiene diluted to 50 mass % with mineral spirit, 9.5 g
of trimethylolpropane triacrylate, 3.8 g of divinylbenzene and 0.67
g of azobisisobutylonitrile (AIBN) were added. The mixture was
reacted for 4 hours after addition of the monomers and AIBN, while
1.3 g of dimethylaminoethyl methacrylate, 0.6 g
oftrimethylolpropane triacrylate, 5.81 g of mineral spirit and 0.05
g of AIBN were thereafter added and the mixture was further reacted
for 2 hours. After the reaction was completed by cooling, the
mixture was filtrated and washed with a small quantity of mineral
spirit, thereby obtaining metallic pigment paste. The content of a
nonvolatile component was 52.8 mass %, and the quantity of coating
resin, i.e., the quantity of the coating-layer according to the
present invention was 12.0 g per 100 g of aluminum flakes. The
obtained paste was partially washed/filtrated with hexane,
pulverized by natural seasoning and thereafter passed through a
screen of 100 .mu.m in aperture, for preparing a metallic pigment
for powder coating. This metallic pigment is hereinafter referred
to as a pigment A.
Comparative Example 1
[0100] First, metallic pigment paste (trade name 7640NS by Toyo
Aluminum Kabushiki Kaisha) prepared from paste of aluminum flakes
was washed with mineral spirit and filtrated. The content of a
nonvolatile component in the paste subjected to washing and
filtration was 65.2 mass %.
[0101] 589.4 g of mineral spirit was added to 184.1 g of this paste
in a separable flask of 1 liter and stirred for preparing slurry.
While stirring was continued, the system was purged with nitrogen
gas to be under a nitrogen atmosphere and thereafter heated to
80.degree. C. The following operations were performed while
maintaining these conditions unless otherwise stated.
[0102] 0.92 g of acrylic acid, 9.0 g of epoxidized
1,2-polybutadiene diluted to 50 mass % with mineral spirit, 10.4 g
of trimethylolpropane triacrylate, 4.2 g of divinylbenzene and 0.68
g of azobisisobutylonitrile (AIBN) were added. The mixture was
reacted for 6 hours after addition of the monomers and AIBN. After
the reaction was completed by cooling, the mixture was filtrated
and washed with a small quantity of mineral spirit, thereby
obtaining metallic pigment paste. The content of a nonvolatile
component was 55.7 mass %, and the quantity of coating resin was
14.5 g per 100 g of aluminum flakes. The obtained paste was
partially washed/filtrated with hexane, pulverized by natural
seasoning and thereafter passed through a screen of 100 .mu.m in
aperture, for preparing a metallic pigment for powder coating. This
metallic pigment is hereinafter referred to as a pigment B.
[0103] <Surface Modifier>
[0104] 476 g of perfluorooctyl ethyl acrylate (Light Acrylate
FA-108 by Kyoeisha Chemical Co., Ltd.), 66 g of 2-methacryloyl
oxyethyl acid phosphate (Light Ester P-1M by Kyoeisha Chemical Co.,
Ltd.), 492 g of methyl methacrylate and 4140 g of cyclohexanone
were introduced into a separable flask of 5 liters and sufficiently
stirred for obtaining a homogeneous solution. 10 g of AIBN was
added as a polymerization initiator and stirred/dissolved, and the
system was thereafter sufficiently substituted by nitrogen. The
mixture was stirred and reacted at 60.degree. C. for 20 hr, thereby
obtaining a viscous homogeneous transparent polymer solution. This
solution is hereinafter referred to as a surface modifier solution.
20.3 g of this surface modifier solution was dropped on 1700 ml of
vigorously stirred methanol, for precipitating the polymer. This
dispersion was centrifuged, thereby separating a polymer like gum
and a transparent solution from each other. The obtained polymer
like gum was remelted with 25 g of acetone and dropped on 1500 ml
of vigorously stirred hexane, for precipitating the polymer. This
was recovered by filtration and thereafter vacuum-dried, thereby
obtaining 3.1 g of polymer. From this result, the polymer
concentration in the aforementioned surface modifier solution was
calculated as 15.4 mass %.
Example 2
[0105] 3.6 g of the said surface modifier solution was diluted with
66.0 g of cyclohexanone, added to 70.0 g of the paste obtained in
Example 1 and kneaded at the room temperature for 20 minutes for
obtaining slurry. The obtained slurry was introduced little by
little into 1 liter of vigorously stirred heptane and dispersed. A
cake obtained after filtrating the dispersion and
washing/filtrating the same with heptane was spread on a vat and
naturally seasoned for one night. Dried metallic pigment powder was
passed through a screen of 100 .mu.m in aperture for obtaining a
metallic pigment for powder coating. This metallic pigment is
hereinafter referred to as a pigment C. Table 1 shows the quantity
(mass %) of the surface modifier with respect to the metallic
pigment in the pigment C.
Comparative Example 2
[0106] 21.7 g of the said surface modifier solution was diluted
with 252.8 g of cyclohexanone, added to 400.0 g of the paste
obtained in comparative example 1 and kneaded at the room
temperature for 20 minutes for obtaining slurry. The obtained
slurry was introduced little by little into 2.3 liters of
vigorously stirred heptane and dispersed. A cake obtained after
filtrating the dispersion and washing/filtrating the same with
heptane was spread on a vat and naturally seasoned for one night.
Dried metallic pigment powder was passed through a screen of 100
.mu.m in aperture for obtaining a metallic pigment for powder
coating. This metallic pigment is hereinafter referred to as a
pigment D. Table 1 shows the quantity (mass %) of the surface
modifier with respect to the metallic pigment in the pigment D.
Comparative Example 3
[0107] Metallic pigment paste (trade name 7640NS by Toyo Aluminum
Kabushiki Kaisha) prepared from paste of aluminum flakes was washed
with mineral spirit and filtrated. The content of a nonvolatile
component in the paste subjected to washing and filtration was 70.2
mass %.
[0108] 27.3 g of the said surface modifier solution was diluted
with 360.1 g of cyclohexanone, added to 400.0 g of the paste
obtained in comparative example 1 and kneaded at the room
temperature for 20 minutes for obtaining slurry. The obtained
slurry was introduced little by little into 2.3 liters of
vigorously stirred heptane and dispersed. A cake obtained after
filtrating the dispersion and washing/filtrating the same with
heptane was spread on a vat and naturally seasoned for one night.
Dried metallic pigment powder was passed through a screen of 100
.mu.m in aperture for obtaining a metallic pigment for powder
coating. This metallic pigment is hereinafter referred to as a
pigment E. Table 1 shows the quantity (mass %) of the surface
modifier with respect to the metallic pigment in the pigment E.
[0109] <Preparation of Powder Metallic Coating Material and
Powder Coating>
[0110] These metallic pigments (A) to (E) were blended with
polyester-based thermosetting resin powder (trade name Teodur PE
785-900 by Kuboko Paint Co., Ltd.) for preparing powder metallic
coating materials. Blending ratios, i.e., the contents (g) of the
metallic pigments with respect to 100 g of the thermosetting resin
powder were set to satisfy such conditions that coated plates are
completely concealed by the metallic pigments and the surfaces are
smooth. Table 1 shows the blending ratios.
[0111] The obtained powder metallic coating materials were applied
to substrates formed by tin plates having sizes of 100 by 200 mm
with a corona discharge electrostatic powder coater (MXR-100VT-mini
by Matsuo Sangyo Co., Ltd.) under a condition of an applied voltage
of 80 kV and baked at 190.degree. C. for 20 minutes, thereby
preparing coated plates.
[0112] <Evaluation of Brightness of Coating Film>
[0113] Actual L values of coating films formed on the coated plates
were measured at observation angles .theta. of 15 degrees, 25
degrees, 45 degrees, 75 degrees and 110 degrees with a
spectrophotometer (trade name "X-Rite MA-68" by X-Rite). Then,
values of .beta./.alpha. were calculated from the measured values
on the basis of the following expression (1), for evaluating
brightness of the coating films. Brightness is improved as
.beta./.alpha. is increased. L=[.beta./(.theta.2+.alpha.)]+.gamma.
Expression (1) Table 1 shows the obtained values of
.beta./.alpha..
[0114] In the expression (1), L represents a lightness index
(L*a*b* colorimetric system which is a calorimetric system based on
a uniform color space set by CIE in 1976) measured with a
spectrophotometer (trade name "X-Rite MA68" by X-Rite) at an
observation angle .theta., .theta. represents the observation
angle, and .alpha., .beta. and .gamma. represent constants.
[0115] In order to calculate .beta./.alpha., .alpha., .beta. and
.gamma. must be first decided. Therefore, .alpha., .beta. and
.gamma. were decided by the method of least squares by measuring
actual L values at observation angles .theta. of 15 degrees, 25
degrees, 45 degrees, 75 degrees and 110 degrees and assuming that
the relation between these .theta. and L values satisfies the
expression (1).
[0116] <Corrosion Resistance Evaluation>
[0117] Corrosion resistance of the coated plates prepared in the
above was evaluated through alkali resistance. The coated plates
obtained by the aforementioned coating method were dipped in 0.1 N
of aqueous NaOH solution at 55.degree. C. for 4 hours. Thereafter
the coated plates were washed with water, dried and subjected to
color measuring through the aforementioned method. From the values
of .beta./.alpha. before and after dipping in the alkaline
solution, alkali resistance was evaluated as brilliance retention
according to an expression (2): Brilliance Retention
(%)=(.beta./.alpha. after dipping in alkaline
solution)/(.beta./.alpha. before dipping in alkaline
solution).times.100 Expression (2)
[0118] Table 1 shows the results. TABLE-US-00001 TABLE 1
Comparative Comparative Comparative Example 1 Example 2 Example 1
Example 2 Example 3 Blended Pigment Pigment A Pigment C Pigment B
Pigment D Pigment E Quantity of Coating Resin 12.0 12.0 14.5 14.5
0.0 (g) with respect to 100 g of Aluminum Flakes Quantity of
Surface 0.0 1.5 0.0 1.5 1.5 Modifier (mass %) with respect to
Metallic Pigment Content of Metallic 5 7 9 5 7.5 Pigment (PHR) with
respect to 100 g of Thermosetting Resin Powder Brilliance of
Coating Film 149.2 294.8 154.0 247.4 303.8 (.beta./.alpha.)
Brilliance Retention (%) 79 77 70 67 58
[0119] From the results shown in Table 1, brilliance and corrosion
resistance of the coating film are not reduced in Example 1
provided with the coating-layer according to the present invention
as compared with comparative example 1 provided with the
coating-layer formed by polymerizing the monomer having no basic
group, and the corrosion resistance is superior as compared with
comparative example 1. In Example 2 prepared by providing the
coating-layer according to the present invention and thereafter
further providing the surface modifier layer, brilliance and
corrosion resistance of the coating film are remarkably superior as
compared with comparative example 2 prepared by providing the
coating-layer formed by polymerizing the monomer having no basic
group and thereafter further providing the surface modifier layer,
and the corrosion resistance is remarkably superior also as
compared with comparative example 3 prepared by providing the
surface modifier layer without providing the coating-layer.
[0120] Thus, it is understood that the metallic pigment according
to the present invention is a metallic pigment exhibiting excellent
corrosion resistance also when the surface modifier layer is
provided for improving brightness, for obtaining a coating film
compatibly having high brightness and corrosion resistance.
[0121] The embodiment and Examples disclosed this time must be
considered illustrative in all points and not restrictive. The
range of the present invention is shown not by the above
description but by the scope of claim for patent, and it is
intended that all modifications within the meaning and range
equivalent to the scope of claim for patent are included.
INDUSTRIAL APPLICABILITY
[0122] The metallic pigment according to the present invention is
preferably applicable to a coating material, particularly a powder
coating material, and can simultaneously supply excellent corrosion
resistance without damaging metallic feel and high brightness in a
case of forming the surface modifier layer.
* * * * *